A torque cam device arranged to generate a torque in accordance with a difference of rotation phases of two cam member is used in various fields. One of these torque cam mechanisms is an end cam device which includes cam surfaces which are positioned at ends of two annular or cylindrical cam members, and which have, respectively, helical cam surfaces. In this end cam device, the two cam members are disposed coaxially with each other so that these cam surfaces are slidably abutted on each other. In this device, by providing the difference of the rotation phases to the two cam members, the two cam members are arranged to be moved to closer to or away from each other while the cam surfaces are slid on each other, so that the entire length (the axial length) is varied. Moreover, the force in the rotation axis direction (the thrust) is generated.
The thrust generated by this torque cam device is determined by the inclination angle α of the cam surface, an input toque T for providing the difference of the rotation phases, a radius R of the cam contacting portions (the entire length of the cam surfaces), and a frictional coefficient μ of the cam surfaces, as shown in a following equation (1) (cf. a patent document 1).F=T/R/tan(α+tan−1 μ)  (1)
On the other hand, it is conceivable that the above-described torque cam device is used for a movement of a movable pulley of a belt-type continuously variable transmission mechanism for a vehicle (varying a winding radius of the belt), and for generating a clamping force (axial thrust of the pulley) for clamping the belt.
For example, FIG. 10 is a configuration view schematically showing a configuration which is invented in a process during which the present invention is devised, and in which the torque cam mechanism is applied to the belt-type continuously variable shift mechanism. As shown in FIG. 10, the belt-type continuously variable transmission includes a primary pulley 130P, a secondary pulley 130S, and a belt 137 wound around these pulleys 130P and 130S, and arranged to transmit the power. In this case, the torque cam mechanism 109 is provided to the secondary pulley 130S.
The secondary pulley 130S includes a fixed pulley 134 having an integral configuration with the rotation shaft 136, and a movable pulley 135 which is disposed coaxially with the fixed pulley 134, and which is arranged to be moved with respect to the fixed pulley 134 in the axial direction and in the rotation direction.
The torque cam mechanism 109 is an end cam. The torque cam mechanism 109 includes a drive cam member 191 disposed and fixed on a back surface of the movable pulley 135; a driven cam member 192 which is adjacent to the drive cam member 191, and which is disposed and fixed on a rotation shaft 136 of the fixed pulley 134; a cam surface 191a which is provided on one end surface of the drive cam member 191; a cam surface 192a which is provided on one end surface of the driven cam member 192; and a ball 193 which is disposed between portions between the both cam surfaces 191a and 192a. The torque cam mechanism 109 is constituted as a ball torque cam mechanism. The drive cam member 191 and the driven cam member 192 is formed into an annular shape or a cylindrical shape.
As shown in FIG. 11(a), these cam surfaces 191a and 192a are divided, respectively, into four of two drive cam surfaces (driving cam surfaces) 191d and 192d and two driven cam surfaces (coast cam surfaces) 191c and 192c. FIG. 11(b) is a side view showing a state in which the annular drive cam member 191 and the annular driven cam member 192 are deployed. As shown in FIG. 11(b), the drive cam surfaces 191d and 192d and the driven cam surfaces 191c and 192c are inclination surfaces which are inclined in different directions. The respective drive cam surfaces 191d and 192d are parallel to each other. The respective driven cam surfaces 191c and 192c are parallel to each other.
In this way, the drive cam member 191 and the driven cam member 192 have, respectively, two of the drive cam surfaces 191d and 192d, and two driven cam surfaces 191c and 192c. This is because the torque cam mechanism 109 is acted to the movable pulley 135 to be eccentric from the center of the rotation by one drive cam surface and one driven cam surface, so that the movable pulley 135 is inclined. Accordingly, there are equally provided two drive cam surfaces 191d and 192d and two driven cam surfaces 191c and 192c, so that the cam is not acted to the movable pulley 135 in the eccentric manner.
In the belt-type continuously variable transmission mechanism for the vehicle which is provided with this torque cam mechanism, when the input torque transmitted from the belt 137 to the secondary pulley 130S is increased, the belt clamping fore of the secondary pulley 130S becomes deficient. The fixed pulley 134 of the secondary pulley 130S is slipped with respect to the belt 137. Besides, the movable pulley 135 which can be rotated relative to the rotation shaft 136 follows the belt 137. Accordingly, the delay of the rotation phase of the fixed pulley 134 with respect to the movable pulley 135 is generated.
With this, the drive cam member 191 fixed to the movable pulley 135 is rotated relative to the driven cam member 192 fixed to the fixed pulley 134. The drive cam member 191 is moved from a state shown by a broken line in the rotation direction and in the axial direction as shown by a solid line of FIG. 11(b) while sliding the both drive cam surfaces 191d and 192 through the balls 193, so that the movable pulley 135 is moved closer to the fixed pulley 134. Consequently, the groove width of the V groove of the secondary pulley 130S is decreased, so that the belt clamping force is increased. Therefore, the slippage of the fixed pulley 134 is dissolved.
Conversely, in a state where the driving source acts the negative input torque (the braking torque), the delay of the rotation phase of the fixed pulley 134 is dissolved. When the belt clamping force of the secondary pulley 130S becomes deficient with respect to the negative input torque, the antecedence (precedence) of the fixed pulley 134 with respect to the movable pulley 135 is generated. In this case, the drive cam member 191 of the movable pulley 135 is delayed with respect to the driven cam member 192 of the fixed pulley 134. The drive cam member 191 is moved from a state shown by the broken line in the rotation direction and in the axial direction as shown by a two dot chain line of FIG. 11(b) while sliding the both driven cam surfaces 191c and 192c through the balls 193, so that the movable pulley 135 is moved closer to the fixed pulley 134. Consequently, the groove width of the V groove of the secondary pulley 130S is decreased, so that the belt clamping force is increased. Therefore, the slippage of the fixed pulley 134 is dissolved.
In the torque cam mechanism 109, it is desired to sufficiently ensure the thrust F generated by the torque cam mechanism so as to obtain the belt clamping force which has no trouble (is not interfered) with the torque transmission by the belt 137, and to sufficiently ensure the pulley slide amount S shown in FIG. 11(b).
As shown by the above-described equation (1), the generated thrust F is determined by the inclination angle α of the cam surface, the input torque T, the radius R of the cam contact portions, and the frictional coefficient μ of the cam surfaces. The input torque T is varied by the running condition of the vehicle, and the condition of the road. The input torque T is not operated in the same way. For further increasing the generated thrust F, it is efficient to decrease the inclination angle α of the cam surfaces (cf. FIG. 11(b)), and to decrease the frictional coefficient μ of the cam contacting portions, and to increase the radius R of the cam contacting portions.
In a case where the inclination angle α of the cam surface is decreased, it is necessary to increase the circumferential length of the cam surface for ensuring the pulley stroke amount necessary for the shift. Accordingly, the radius R of the cam contacting portions is increased. If the radius R of the cam contacting portions is increased, it is possible to further increase the generated thrust F. However, it is necessary that the drive cam surface and the driven cam surface are received between the pulley shafts. The distance of the radius R is limited. The inclination angle of the cam surface is limited. Therefore, the decrease of the inclination angle α is limited.
Moreover, it is effective to decrease the frictional coefficient of the cam contacting portion. However, the contacting itself has a mechanical properties. This is limited.
Accordingly, the use of the end cam such as the torque cam mechanism 109 is limited to the scooter and the small vehicle such as the light car which have the driving source having the small torque. Alternatively, the use of the end cam such as the torque cam mechanism 109 is limited to the use together with the general method of operating the movable pulley by using the hydraulic pressure. Accordingly, it is requested to develop the torque cam device which can use in the vehicle having the driving source having the larger torque without using together with the hydraulic method and so on.